Patent GB-994995-A (GB)
Title: Apparatus for controlling the position of a floating vessel
IPC: G05D1/02
Filed: 1962-03-12
Abstract: 994,995. Automatic position control of floating vessels. SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ N.V. March 12, 1962 [March 14, 1961], No. 9429/62. Heading G3R. In a system for automatically maintaining a desired position and heading of a floating vessel, error responsive means located on the vessel control the direction and magnitude of propulsive thrusts applied at two points spaced from the centre of rotation of the vessel. In Fig. 1 the position of a ship 10 relative to a desired position, e.g. for an offshore drilling operation, is determined by the angles X and Y which an anchored line 13 subtends in mutually perpendicular longitudinal and lateral vertical planes. Electrical signals dependent on these angles, produced by a pair of potentiometers operated by a gimbal mounted pendulum (not shown), are utilised to control the orientation and thrust of electrically driven propellers 11 and 12 which are adjusted about vertical axes at each end of the ship to restore the ship to its desired position. The magnitude of the signals may be adjustable and integral and differential components may be added. In addition the orientation and thrust of the propellers may be controlled manually. Lateral position. In Fig. 3 the electric signal representing deviation in a lateral direction is applied to an actuator 130, which may be hydraulic, to adjust the position of the axis of a pinion 120 and thus slide two racks 111, 115 in the same direction relative to a U-shaped base 113. Arms 110,114 attached to the slides move contacts, e.g. 77, relative to resolver discs 70, 71 each having two conducting segments, e.g. 73, 74, separated by an insulating strip, e.g. 76, which is wide along one radius. Movement of contact 77 on to one or other of segments 73 or 74 energizes a relay 82 or 83 to run a motor (not shown) which rotates one of the propellers in one or other direction about its vertical axis. A synchro transmitter (not shown) also moved with the propeller, is connected to a synchro receiver 30 which rotates disc 70 so as to provide follow-up by restoring contact 77 to insulating strip 76. Movement of the contact associated with disc 71 similarly controls the orientation of the other propeller and the adjustment of the two propellers is such as to correct the lateral position of the ship. Thrust of the propellers is also made dependent on the extent of movement of the contacts relative to the centre of dics 70 and 71 by causing such movement to move cables, e.g. 104, which vary the energization of eddy current couplings (not shown) between the propellers and their driving motors. Longitudinal position. The electric signal representing deviation in a longitudinal direction is applied to actuator 140 which moves base 113 and thus the contacts associated with discs 70, 71 in a direction perpendicular to actuator 130 so that the orientation and thrust of the propellers is adjusted to move the ship backwards or forwards as necessary to correct its position. The relative position of discs 70, 71 is adjustable by operating a turnbuckle 153 so that the propellers may be arranged to rotate slowly in opposite directions when the ship is in its correct position. Heading. An electric signal from a gyromagnetic compass representing deviation in the ship's heading is applied to an actuator 121 which moves rack 115 in one direction and, because of pinion 120, rack 111 in the opposite direction. This adjusts the orientation and thrust of the propellers so that the ship is turned about a vertical axis to correct its heading. Manual control. A knob 132 may be operated to move racks 111 in two directions at right angles to permit manual control of the lateral and longitudinal position of the ship. Rotation of knob 132 moves the racks in opposite directions for manual control of heading. Alternatively manual control in the three senses may be obtained by a single handle operating three potentiometers the signals from which are substituted for those applied to actuators 121,130,140. Modifications. Use of analogue type resolvers and radio or radar position locating devices are referred to.